Photoreceptor degenerative diseases afflict 50,000 to 100,000 individuals in the United States. This proposal focuses on the gene for RDS/Peripherin, in which mutations are known to cause photoreceptor degeneration. The long-term objectives are (1) to elucidate the mechanisms(s) by which mutations in RDS/Peripherin lead to retinal degenerative diseases and (2) to better understand the function of RDS/Peripherin in normal rod outer segments. The proposed research plan is to generate a series of disease-linked RDS/Peripherin mutants and investigate structure and function. To this end, for specific aim 1, both in vivo and in vitro approaches will be used to assay for (1) correct membrane topography, (2) core glycosylation, (3) homodimer formation, and (4) association with ROM1 protein. Specific aim 2 investigates the functional consequences of disease-causing RDS/Peripherin mutants in terms of their role in membrane fusion. Mutants will be tested for their ability to participate in ROS membrane fusion using a resonance energy transfer assay. A series of C-terminal mutants will be generated and studied to identify the regions of RDS/Peripherin necessary for membrane fusion. The role of RDS/Peripherin: ROM1 complex in membrane fusion will be studied. Finally, for aim 3, additional retinal proteins that interact with RDS/Peripherin will be identified using the yeast two-hybrid system.